The roof of a building is the upper structure of the systems providing a variety of structural functions. The roof structures outer layer is composed of a variety of modular materials that overlay or interlock. The purpose of the outer layer (roof) is to protect the interior of the building from harmful weather and damaging effect from the sun.
Roofing materials are typically chosen based on local weather conditions, availability of local resources and the ease of installation. This is why often materials as varied as thatch and ceramic tile are used throughout the world. Metal, slate, and asphalt are the most common modern roof materials. Of the three, asphalt is the most widely used residential roof material due to the relatively low cost of petrochemical used in its construction and ease of installation.
Energy efficiency is the measure of a system to do the same amount of work with less work and is often confused with energy conservation. Over the course of time materials have been engineered to provider greater energy efficiency. One efficiency metric that is widely used is thermal resistance, commonly call R or R value. Thermal resistance (R) is the capacity of a material to resist heat flow. The greater the R value the greater the efficiency of the given material. Wood shingles for example have an R value of 0.97, whereas asphalt shingles have an R value of 0.44. Another important metric with respect to roof material is the solar reflectance Index (SRI). SRI is the measure of the ability of a given material to reflect solar energy from its surface back into the atmosphere. SRI is particularly important in warm climates and climate that have high solar exposure. Consider together R and SRI values are good measures to evaluate performance of a material in given condition one measures transmission while the other measures load.
Modern asphalt energy efficient shingles are commonly composite tiles that incorporate fiberglass and reflective granular materials. While these materials are more energy efficient they are typically more expensive and require the old roof tile to be removed before installing the new roof tile. Considering the functional requirements roofs must meet, varied environmental conditions (cold-warm), varied solar conditions, low cost, ease of installation and energy efficiency asphalt roof are a good solution. However, improvements can be made.
Polyurethane foam is a versatile material that can be molded, sprayed and poured. It can be formulated to achieve a wide range of structural, insulating and acoustic applications. Closed cell polyurethane foam is widely used as an insulating building material. The material in inert when cured and emits low volatile organic compounds. Polyurethane foam is formed by chemical reaction of typically, methylene diphenyl diisocyanate and polymeric methylene diphenyl diisocyanate commonly referred to as the A side and typically a blend of polyols and other agents that give performance characteristics commonly referred to as the B side. Given the wide range of structural and insulating properties of polyurethane foam with its ability to be molded it is a good candidate material for a modular roof tile substrate.
Polyurea elastomer and polyurethane copolymers are used in a variety of coating applications and have very good tensile, shear and elongation strength. They perform in thermal extremes and can be blended with materials that have very high SRI values. Additionally, low cost polyurea have been created that have self-healing properties.
Glass microspheres are low density additives used in paint that have been shown to have 80-86% SRI in elastomeric paint.